Three Zs

I've run a search on piston slap and can't find a definitive answer. My "02 is in the shop now for what I suspect is piston slap. I've heard that GM's reaction runs anywhere from "it's normal" to replacing the engine. I really don't want these guys doing any serious work on the engine unless it's really needed. If my problem is piston slap, should it be fixed? The car runs strong, but it does some serious knocking until it warms up.

Thanks

Dave C. '04 Z06

I think what's commonly defined as piston slap is actually the piston rocking in it's bore slightly. This is a common problem with cars with forged pistons when the engine is cold, but hypereutetic pistons normally fit tight enough to where you shouldn't get it. But alas, GM mass produces motors and sometimes a slightly wrong sized piston gets stuck in a slightly bigger bore.

That being said, it's really no problem..as long as it's minor it shouldn't hurt anything as long as it goes away once the car is warmed up. And that's the other reason why you always want to warm up a car well before you beat on it.

Also, there is a common issue with the LS6 that the motors have a tapping noise around 1500-2500 RPMs. This is not piston slap, but valve train noise. This also isn't an issue as long as it's not ridiculously loud. It comes, I believe, from the valve spring pressure and the lifters compressing slightly during operation. LT-1 engines had this same problem, but even though thier cam wasn't as high a lift, the springs were at almost max capacity at fully open with the stock cam so you'd get the same sort of noise, more so when the engine was warm and the oil had thinned out.

-Dave C. '04 Z06

PS: So basically, I wouldn't worry about it unless it's extreme.

EVIL_C5

www.pistonslap.com

rudyarias

I find that my 4 month old Z16 is exhibiting that symptom, it has gotten louder and sounds like my Dad's old Chevy Pickup truck when it hit about sixty thousand miles. In addition, I lose oil pressure during acceleration (when heavy the check gauges light kicks on). My dealer told me that the "noise" is something I have to live with and to keep driving it until the engine "blows up". They can not identify the cause of my oil pressure loss as they show it is within the minimum pressure specifications. They insist that the LS6 has no known issues. That on top of other problems with the car and my dealer's lack of warranty response since I bought it, has me left me frustrated with GM's "world class" sports car.

If I buy another Corvette after this one, it'll be a used one out of warranty. I can at least get the engine running right without having the "void the warranty" threat over my current one.

Dave C. '04 Z06

Although LS6s tick, losing oil pressure is NOT normal, especially to the point where the light kicks on. I run mine pretty hard and the oil pressure is always above 37psi. It's an '04 as well.

I would change the oil just to make sure someone didn't put the wrong type of oil in it, or that your filter isn't plugged up for some reason, and make sure the oil level is correct. The LS6 takes ~ 6.5-7 quarts of oil.

-Dave C. '04 Z06

rudyarias

Oil has been changed and changed. It only goes as high as 36 psi cold, warm 6 to 15 depending on how high the oil temp is. Anyway, this puppy ran hot oil temps not to mention the tranny continually overheating when on the interstate from the day I drove it out of the dealership. Dealer tells me that the spec is 6 psi per 1000 rpm and GM will not do anything till it goes below the spec or the engine blows. I paid to have the GM trans cooler installed by the Dealer and I installed the Lingenfelter Oil Cooler. They helped get the temps down to what is considered normal (without the coolers). The Dealer also informed me that I may have voided my warranty with the non GM oil cooler. Granted my Porsche 928 was no picnic with its nbr 2 & 6 bearing issues, but this Z16 is placing doubts in my mind on GM's standards for quality control and/or engineering-manufacturing philosophies.

WA 2 FST

Find a different dealer. 6psi per 1000rpm is ridiculous. The old rule of thumb is 10psi per 1000rpm, and these motors are so tight as far as tolerances go... I'd be nervous about anything below 30psi at warm idle.

And you definitely do _not_ want pressure going down as revs climb. It should go up slightly.

Then again, if you're under 3/36k warranty then you can drive the crap out of it and if it blows up, you've documented with the dealer that you have a problem.

rudyarias

I have to no avail. The three dealers that have had the car and have acknowledged the low oil pressure but are bound to what GM warranty dictates. The GM minimum spec is 6 psi per 1000 rpm. My regular machine shop tells me that the the valve springs and oil pump O rings are the LS6's Achilles heel.

agentf1

Was all of this verified with a real guage? I don't trust factory guages.

RoHo

I have never been one to look for a fix in a bottle, but my neighbor has an LS1 in his Impala with that problem and the dealers gave him that same run around, he put in a bottle of PRO LONG engine treatment and it went away. He now just adds a bottle when he changes oil. It may be worth a try if the dealer won't stand behind it.

chiefDave

That is and any mechanic shoud raise the flag, esp on a Z06! High temps + Low pressure = huge friction and $$$. Waiting for a motor to blow is even worse, and IMO call your laywer and have him/her contact the dealer who told you that and get it on hard copy. I just don't get some dealers I have one great one in town, and one who sucks a$$. Good luck
Dave

junkmn

Call your local factory regional manager. You should be able to locate a number via the web or through a Chevy 800 number. I had a transmisiion in my SUV that was making excrutiating whining noise at 60 mh. I kept geting the dealer run around. Called the rep. Within a few days I received a call that I was getting a new transmission. Delaers do not like to spend money if they don't have to. Even worse for them is to get complaints to Corporate. Push it, you will get what you want/need.

rudyarias

They each used mechanical gauges on it to verify the pressure. Its more of a rattle/cladder noise than a "tick" at the 1500/2500 rpm range. My regular mechanic is convinced its a rod bearing issue because of the noise it makes from a cold start. I called GM's Customer Service who told me that the oil sender was replaced twice by my dealer. The CS person also told me that because it shows in their computer that the diagnotics showed the engine within GM specs, they could not do anything more than make an appointment with another dealer in my area.

Three Zs

Thanks Dave...what you say makes sense. The factory is not going to do anything about it anyway, but I think they're right in this case.
Appreciate the advice.

rudyarias

Interesting TSB posted on http://www.pistonslap.com/tsb/020601038.htm

Talks about the Oil Pump O ring failure causing what Dave describes

game on

my 02 z06 with oil pressure warm (180 degrees) is at 30 psi. Goes up with rpm to 50s.

If I ever see less than 20 psi at idle (temp high or low), I will shut it down and have it hauled.

Why is GM using a dry sump system with the C6 Z06? Oil pressure/flow problem? Casual observations on the internet, the C5R bock with solid lifter setup has oil pressure issues. Cylinders 7 and 8 have starvation issues.

If you have been seeing 6psi at idle, press for a new engine because you most likely have bearing issues. Getting the pressure back up with a new oil pump, etc. will not fix any damage that has already been done to the main, rod and cam bearings from low oil pressure.

I currently have an issue with the transmission in 02 Z06 and will stand hard with my belief that it needs to be replaced. The dealership wants to replace a bunch of parts to fix a reverse gear engagement issue. So how much metal from this issue has caused damaged to other gears that will show up in the future? I've told them not to the fix and it can sit there forever as far as I am concerned. Great car, just needs the great GM service advertised on TV and the promises during the buying process.

My 2cents worth.

rudyarias

Before my oil cooler, the oil temps would hover around 295º-325º, now they're hovering around 228º, even when I'm out in the (balmy single digit) Chicago winter weather. I'm working on getting the block repaired as it would impair the car's long term value with the serial numbers being out of sync if the engine is replaced.

The "wet" sump in the LS6 requires to be a quart over if the car is to be driven on a road course. The Carrousel at Road America has acquired the nickname of "Corvette Killer" over the years. Oil starvation is a common experience by the G forces at that particular section of the track with "wet" sump engines found in our cars. Dry sump eliminates the issue.

MaverickC5

I would visit another dealer. Or call the Cheverolet Zone Office.

rudyarias

Have been working on the Zone Office to have someone ride with me till it gets to its normal operating temp then do their tests. I think the problem is that the car left in the dealer's repair shop to be diagnosis, compounded by the Chicago balmy single digit weather. Has kept the car from reaching its operating temps thus showing the minimum specification for oil pressures when the engine is luke warm.

I also believe that most GM dealers in my area are afraid of being "dinked" by GM for their warranty billing/work. GM apparently is on a campaign in my area to quash dealers who look for TSB (Technical Service Bulletins) work when a car comes in for service/maintenance. From what I understand, the amount of warranty/TSB work a dealer does, reflects on how much money they will make in selling new cars. The less they bill for warranty/TSB work, they more they make from sales.

MaverickC5

I also believe that most GM dealers in my area are afraid of being "dinked" by GM for their warranty billing/work. GM apparently is on a campaign in my area to quash dealers who look for TSB (Technical Service Bulletins) work when a car comes in for service/maintenance. From what I understand, the amount of warranty/TSB work a dealer does, reflects on how much money they will make in selling new cars. The less they bill for warranty/TSB work, they more they make from sales.


Based onthe serice that I have had with GM, it seems to vary by dealer. I will go to another store until I find the one that wants to take interest. Now they get all mycvehicle business . All my cars areservied well. Push the Zone manager , if he expects to keep his sales volume up in your area he will not let GM get any bad PR. I say "work 'em".